Recently, coolants used in car air conditioners and the like are being changed from CFC gas to carbon dioxide gas for the sake of environmental impact, and structures for shaft sealing carbon dioxide gas as a sealed fluid have been becoming more common. However, in cases in which carbon dioxide gas is used for the coolant, the sealed fluid that will be the coolant is set to higher pressures than have been used in the past. There has arisen an urgent need to improve the sealing strength of the shaft sealing portion, and various seal devices having high sealing strength have been developed as lip seals for compressors in car air conditioners.
One example is a lip seal device (see FIG. 10) disclosed in Utility Model Application No. 3-41264 (Patent Document 1).
In this lip seal device, a backup ring 103 made of a metal material and having a ring shape is disposed between a rotating shaft 102 and an internal peripheral surface on the atmosphere side of a seal lip 101, the backup ring 103 being fitted in light contact with the internal peripheral surface of the seal lip 101. Furthermore, an annular part 104 made of a resin material is disposed in the same shape as the backup ring 103 on the atmosphere side B of the backup ring 103. Furthermore, on a fluid storage chamber side A of the backup ring 103, a seal surface 107a firmly bonded to the external peripheral surface of the rotating shaft 102 is provided to an end part 107 at which the seal lip 101 extends slantwise towards the fluid storage chamber from a proximal part 106 in which a reinforcing ring 105 is embedded, and a garter spring 108 for subjecting the seal surface 107a to tension is mounted in an annular groove provided to the external peripheral surface of the end part 107.
A ring-shaped support plate 109 is disposed on the atmosphere side of the annular part 104, and the backup ring 103, the annular part 104, and the support plate 109 are sandwiched together by a holding ring 110 whose external periphery has a U shape in cross section. These three sandwiched components collectively are a sealing part that reinforces the aligned seal lip 101.
The distance between the annular groove and the seal surface 107a at the distal end of the seal lip 101 must be reliably manufactured, but the seal lip 101 easily deforms, being made of rubber, and it is difficult to ensure the dimension of this distance when the rubber is molded. Furthermore, the backup ring 103 and the seal lip 101 must be reliably joined together, and when the backup ring 103 is pressed into the seal lip 101, the sealing capacity is compromised because the seal lip 101 is lifted up off the external peripheral surface of the rotating shaft.
To resolve this variety of problems, techniques have been developed such as those demonstrated in Japanese Patent No. 3346743 (Patent Document 2) and Japanese Laid-open Patent Application No. 2003-120821 (Patent Document 3). In the disclosed techniques, an inclined supporting part of a backup ring is press-fitted into a tapered surface in a seal lip to expand the diameter of the sealing part surface, the enlarged tapered surface of the inclined seal lip is held in pressured contact by the inclined supporting part, and the sealing part surface on the atmosphere side is maintained at a constant angle. According to this type of configuration, the sealing part surface held under tension by the backup ring is firmly bonded with sharp surface pressure to the external peripheral surface of the shaft, the sealing part surface is in contact with the shaft across a small contact surface area, the sealing capacity is effectively prevented from decreasing as a result of abnormal deformation in which the sealing part surface is jammed, the state of the sealing corner being in contact under sharp surface pressure is maintained, and excellent sealing capacity is exhibited.
Patent Document 1: Utility Model Application No. 3-41264 (pg. 1, FIG. 1)
Patent Document 2: Japanese Patent No. 3346743 (pg. 2, FIG. 2)
Patent Document 3: Japanese Laid-open Patent Application No. 2003-120821 (pg. 2, FIG. 1)